Abstract
Entanglement is perhaps the most important new feature of the quantum world. It is expressed in quantum theory by the joint measurement formula. We prove the formula for projection valued observables from a plausible assumption, which for spacelike separated measurements is a consequence of causality. State reduction is simply a way to express the joint measurement formula after one measurement has been made, and its result known.
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Macdonald, A. Entanglement, Joint Measurement, and State Reduction. International Journal of Theoretical Physics 42, 943–953 (2003). https://doi.org/10.1023/A:1025414305027
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DOI: https://doi.org/10.1023/A:1025414305027